A bumper apparatus including a bumper reinforcement is attached to a front and rear of a vehicle for minimizing shock impact to an occupant and to a vehicle body by absorbing and reducing collision energy transmitted to the vehicle body as much as possible at the time of a front or rear collision of a vehicle. The bumper reinforcement extends in a vehicle width direction. The bumper apparatus for the vehicle includes an energy absorber made of elastic material such as urethane foam, of which its main object is to protect pedestrians, a bumper reinforcement for holding the energy absorber and for absorbing large collision energy by self-deformation, and a bumper stay for fixing the bumper reinforcement to a vehicle body (for example, to a side member).
The bumper reinforcement, which extends in the vehicle width direction, plays an important role in absorption of large collision energy at the time of the front or rear collision of the vehicle. A bumper reinforcement made of extruded shape of aluminum alloy, instead of steel, is suggested in JP2003-312399A and JPH7 (1995)-215146A in order to improve fuel efficiency by weight reduction of the vehicle. However, costs of such an extruded shape tends to be higher than steel.
The bumper reinforcement needs to efficiently absorb the collision energy at the time of an oblique collision (with a barrier having an angle of 30 degrees) and a frontal collision including a collision with a pole. In other words, it is generally preferable for a stroke-load diagram to have a shape similar to a rectangular wave. However, in a load diagram of conventional one, a value of a load against increase of a stroke decreases as the stroke increases. Accordingly, it is difficult to say that the conventional one is highly efficient. In particular, the conventional one has a disadvantage in absorption of the collision energy at the time of oblique collision.
A need thus exists for a bumper reinforcement made of a steel plate, which has improved efficiency in absorption of collision energy in particular at the time of oblique collision. The present invention has been made in view of the above circumstances and provides such a bumper reinforcement.